The present invention relates to a high efficiency, high work coefficient fan which can be used, for example, in electronics cooling applications. More particularly, the present invention relates to such a fan which comprises an impeller and an outlet guide vane assembly that can each be manufactured using an injection molding, casting or similar technique.
Many prior art cooling fans include a motor-driven impeller which propels a stream of air through a fan housing. These fans may also comprise an outlet guide vane assembly positioned downstream of the impeller to both de-swirl and increase the static pressure of the air. The impeller and the outlet guide vane assembly each include a plurality of radially extending blades or vanes. The shape of each blade or vane can be defined by the values of camber, chord and stagger for each of a plurality of radially spaced airfoil segments in the blade or vane and the degrees of lean and bow for each of the leading and trailing edges of the blade or vane. In addition, the overall configuration of the impeller and the outlet guide vane assembly can be defined in terms of the solidity and aspect ratio of the blades or vanes as a whole.
In designing an impeller or an outlet guide vane assembly for a particular cooling fan, the blades and vanes are usually configured to enable the fan to meet pre-determined performance criteria. However, this can result in the blades or vanes having relatively complex three-dimensional shapes which are difficult to manufacture. In particular, a problem with some prior art cooling fans is the inability of the impeller and the outlet guide vane assembly to be manufactured using an injection molding technique, which is a preferred method for achieving high part yields at low cost.
Referring to FIGS. 3A and 3B, for example, which depict a prior art impeller blade from the forward looking aft and the aft looking forward positions, respectively, one can see that the high degree of trailing edge camber near the hub results in a portion of the suction surface not being visible from the forward looking aft position. This condition would prevent the impeller from being manufactured using an injection molding process. Also, the overlapping impeller blades of the prior art impeller illustrated in FIG. 5 would prevent the impeller from being manufactured using this same technique. Thus, in order to be able to manufacture an impeller using an injection molding technique, the impeller blades must not overlap and the entire suction surface of each impeller blade must be visible from the forward looking aft position.
Referring to FIGS. 8A and 8B, which depict a prior art outlet guide vane from the forward looking aft and the aft looking forward positions, respectively, the high degree of trailing edge camber along the span of the vane prevents the entire suction surface from being seen from the forward looking aft position. Consequently, the outlet guide vane assembly could not be manufactured using an injection molding process. Thus, in order to be able to manufacture an outlet guide vane assembly using an injection molding process, the entire suction surface of each guide vane must be visible from the forward looking aft position. In addition, the flowpath between the leading and trailing edges of the guide vane must have a constant radius.